1. Field of the Invention
The present invention relates generally to a barrel driving system, more particularly, relates to a barrel driving system capable of correcting backlash of zooming system.
2. Description of the Related Art
A zooming barrel structure has multiple barrel sets comprising a driving barrel, a zooming barrel and a focusing barrel, and these barrels have substantially cylinder structures. A first guiding groove and a second guiding groove are arranged in the inner wall of the driving barrel, and a first guiding protrusion is arranged on the outer wall of the zooming barrel, and a second guiding protrusion is arranged on the outer wall of the focusing barrel. During fabrication of the zooming barrel structure, the zooming barrel and the focusing barrel are assembled inside the driving barrel, and the first guiding protrusion is placed into the first guiding groove, and the second guiding protrusion is placed into the second guiding groove.
When the driving barrel is driven to rotate by a motor, the first guiding protrusion and the second guiding protrusion are forced to move along the first guiding groove and the second guiding groove respectively, so that the zooming barrel and the focusing barrel can be moved forward or backward correspondingly along an optical axis. A zooming lens group and a focusing lens group are arranged in the zooming barrel and the focusing barrel respectively. Therefore, a zooming operation and a focusing operation can be performed upon the forward or backward movement of zooming barrel and focusing barrel driven by the clockwise or counterclockwise rotation of the driving barrel controlled by the motor.
In order to check whether the barrel is moved to the correct position, a zoom photo-interrupter (PI) and a home PI are arranged in the zooming barrel structure for position detection. The zoom PI detects the rotation of the motor and a count value is generated upon the detection results. According to the count value, the distance of rotation of the motor can be calculated to derive the actual position of the barrel. The home PI is used to position the initial position of the barrel to prevent an image sensor from being impacted by the barrel while retracting.
For smooth movement of the guiding protrusion in the guiding groove, there is no tight fit between the guiding protrusion and the guiding groove, but a backlash exists. However, the backlash will cause an error between the count value and the actual position of the barrel after the barrel is driven to move forward and backward for many times, and such error decreases the accuracy of the zooming operation and the focusing operation.